Temperature-Dependent Hydrogen Embrittlement of Austenitic Stainless Steel on Phase Transformation

Abstract

A critical issue that needs to be addressed for wider utilization of hydrogen as fuel is protection against hydrogen embrittlement during cryogenic storage as it weakens the microstructure bonding force of metals through hydrogen penetration. Austenitic stainless steel, which is usually used in cryogenic vessels and is well known for its high hydrogen resistance at room temperature, has also been reported to be vulnerable to hydrogen embrittlement under cryogenic temperatures. In addition, because large storage vessels are operated over a wide range of temperatures, material behavior at various temperature conditions should also be considered. Therefore, in the present study, hydrogen charging of austenitic stainless steel was performed under various temperature conditions for carrying out prestrain and tensile tests. A decrease in the tensile strength and elongation and an increase in the yield strength were observed in all cases. In particular, the case of 20% prestrain at cryogenic temperature followed by tensile test at room temperature after hydrogen charging showed fracture in the elastic region. The hydrogen index was evaluated from the perspective of elongation and reduction in area, which are factors that indicate the degree of ductility. The aforementioned case showed the most severe results, while non-prestraining followed by tensile tests at room temperature was the least effected by hydrogen. In addition, the effect of strain-induced martensite on hydrogen embrittlement was analyzed using electron backscattered diffraction (EBSD). It was observed that the higher is the prestrain at cryogenic temperatures, the greater is the volume fraction of α’ martensite, which leads to hydrogen embrittlement. The edges and center of the fracture surface were analyzed using scanning electron microscopy (SEM). The hydrogen-charged specimens exhibited brittle fractures at the edges and ductile fractures at the center. The more severe the embrittlement, the more were the number of intergranular fractures and microdimples observed at the edges.

Effect of Hydrogen Charging on the Mechanical Properties of High-Strength Copper-Base Alloys, Austenitic Stainless Steel AISI 321, Inconel 625 and Ferritic Steel 1.4511

“…Several research papers indicate that for austenitic stainless steels, the resistance to HE increases with the stabilizing of the FCC phase [50][51][52][53][54]. Therefore, both a low M d30 temperature as well as high stacking fault energies above 43 mJ/m 2 improve the resistance to HE since the FCC is stabilized and the formation of deformation twins is postponed.…”